<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>2.34</title>
</head>

<body>
    <script>
        //非严格模式
        function test1(a) {
            arguments[0] = 34;
            console.log(a);
        }

        //严格模式
        function test2(a) {
            "use strict";
            arguments[0] = 34;
            console.log(a);
        }

        function test3(a, b = 10) {
            'use strict';   //会报错
        };

        test1(20);
        test2(20);
        test3(5);

    </script>
</body>

</html>